1. Field of the Invention
This invention relates to an improvement on the imaging system of a camera, notably a digital camera.
2. Description of Related Art
The adjustment of the amount of light in a camera is chiefly made by a combination of a shutter determining exposure time and a stop governing a numerical aperture (such as an F-number). In most cases, the amount of light is controlled by mechanically driving them.
In a shutter with mechanical drive, the simultaneity of exposure over the whole range of the aperture of the shutter itself cannot be ensured. Consequently, when the shutter is not placed in the proximity of the stop, variation of the amount of light in an image plane is caused. In a variable magnification optical system, therefore, it is necessary to move a shutter unit together with an optical system partially moved.
As shutters for fulfilling the condition of the simultaneity of exposure mentioned above, liquid crystal shutters using liquid crystals are known. The liquid crystals, however, have properties that transmittances vary greatly with the directions of vibrations of light waves.
A camera using a physical-property element that the transmittance of light or the amount of transmission of light can be controlled is disclosed in Japanese Patent Kokai No. Hei 6-46324. In this example, light is normally split in such a way that a circular polarization plate is placed on the image side of the physical-property element with the function of linear polarization, and circularly polarized light is incident on a light reflecting means placed behind the polarization plate.
In a single-lens reflex finder camera, a half mirror or a half prism is used. The purpose of this is to conduct light from the imaging optical system into a finder. That is, it is used to split the optical path. In particular, in the type that a monitor image is displayed on a liquid crystal display, it is necessary to always display the image on the liquid crystal display.